ATLANTA — The disproportionately high rate at which black students are suspended from school represents a violation of a civil right inherent in the “American promise” of equal education, Education Secretary Arne Duncan said Tuesday.

Secretary Duncan was speaking after the Department of Education published a new report that found that black students, whether poor or wealthy, are more than three times more likely to receive out-of-school suspensions than white kids in US schools.

“The sad fact is that minority students across America face much harsher discipline than non-minorities, even within the same school," Secretary Duncan said ahead of the announcement of the report at Howard University in Washington.

But racism is not the only possible explanation for the contrast between the discipline meted out to black and white student, say some teacher and parent groups, who add that other factors could also lead to such a disparity.

The Civil Rights Data Collection – contains the reported suspension numbers from 72,000 schools, and no analysis. It looked at a number of potentially related factors, including teacher pay and course offerings at the schools.

But as debate rages over whom, or what, to blame for the high punishment rates for black students, especially boys, the report feeds into a growing body of academic work suggesting that the widening use of suspension for routine or minor infractions, including profanity and dress-code violations, not only undermines student achievement, but carries broader societal costs.

“What this data points out is that schools have a choice, that they can say, ‘It’s tough for us, the topic of race is daunting and awkward for us, but we ought to do something,’ ” says Russ Skiba, an educational psychologist at Indiana University, in Bloomington. “By just laying this data out there, DOE is taking a leadership position on this by getting beyond the post-racial myth,” the mistaken assumption that the US has put racism in its past.

Among several findings in a report that purports to reveal “long-hidden data” about expulsions, the Civil Rights Data Collection said black and Hispanic students make up 70 percent of students referred by school officials to law enforcement. It also gave run-downs of suspension data in some of the nation's largest school districts, most of which told a similar story to Wake County, N.C., where whites make up 57 percent of the population and received 25 percent of suspensions, while blacks make up 24 percent of the student body and received 57 percent of suspensions.

One thing experts do agree on is that the causes for the discrepancies are complex. Some urban schools with the highest suspension and expulsion rates also have high populations of poor black students, a higher-than-average percentage of whom come from single parent families. Other studies have shown that children from such homes are more prone to disciplinary problems.

The report also suggests that the problems are inherent in how American schools are set up, with the lowest paid and least experienced teachers most often working at poorer, urban schools with more discipline problems.

But previous studies have shown that race plays a role in higher suspension rates even when taking into account the other factors, such as poverty and family structure.

One study by Indiana University has suggested that whites more often get suspended for objective behavior issues like smoking in the bathroom, while black kids are more often punished for subjective reasons, including acts of defiance.

At the same time, data suggests that there's little evidence that black children exhibit higher rates of actual deviance than white children. That suggests a cultural causation where a largely white teaching corps may be applying hidden prejudices in discipline, says Professor Skiba. “We've had teachers tell us that there are different forms of white defiance and black defiance, and they're bothered more by black defiance,” he says.

“There is much handwringing from educators about socio-economics and other factors, all of which play some role,” the Washington Post's Robert Pierre wrote recently in reaction to a study on higher punishment rates for blacks in the District of Columbia. “But the more disturbing reason is one that many well-meaning people are loathe to admit: We see them differently. Adults attach to children their views of black men, even when those children are too young to understand that they are anything other than children.”

Such statements underscore research that has found a causal relationship between race and school punishment.

A study in North Carolina showed that black kids were punished more frequently and more harshly than white students for the same offenses. Another Indiana University study, meanwhile, showed that schools that meted out fewer suspensions had higher achievement scores for all groups. And a study in Texas last year found that suspension rates were linked to higher rates of incarceration for minority groups.

“You could have the best intentions in the world for pursuing a practice, but if it's having an adverse impact on one racial group more than another, and evidence suggests that it is, that's what makes it not compliant with civil rights protections, and to continue to do it is discriminatory,” says Daniel Losen, director of the Center for Civil Rights Remedies at UCLA.

In releasing the data on Tuesday, the Education Department said its intent is to allow information to help school districts take a hard look at discipline policies and consider their impact on students of different races.

“These new data categories are a powerful tool to aid schools and districts in crafting policy, and can unleash the power of research to advance reform in schools,” Assistant Secretary for Civil Rights Russlynn Ali said.